Hydrogen Bonding

To solve the question, we need to determine which statement about Calgon is true based on its characteristics and composition.

Calgon, commonly used in water treatment, is primarily composed of sodium hexametaphosphate ( ). It's important to analyze each given statement:

1. Calgon contains the most abundant element by weight in the Earth's crust.
   • The second most abundant element in the Earth's crust is Silicon (Si), whereas Calgon primarily contains phosphorus, oxygen, and sodium.
   • This statement is incorrect as Silicon is not a component of Calgon.
2. It is a polymeric compound and is water soluble.
   • Calgon is indeed a polymeric compound and it easily dissolves in water, which aids in water treatment by preventing the formation of scale.
   • This statement is correct.
3. It is also known as Graham's salt.
   • The name "Graham's salt" often refers to sodium hexametaphosphate, another name for Calgon.
   • This statement is correct.
4. It does not remove ion by precipitation.
   • Calgon sequesters calcium ions, preventing them from precipitating as scale. It operates by complexing with calcium ions, rather than by precipitation.
   • This statement is correct.

By analyzing each statement, we can conclude that the statement "Calgon contains the most abundant element by weight in the Earth's crust" is true.

Thus, the correct answer is the first option: "

Calgon contains the most abundant element by weight in the Earth's crust.".

Hydrogen bonding in water is influenced by the structural arrangement and the presence of impurities:
- Ice: In ice, water molecules are arranged in a crystalline structure with extensive hydrogen bonding. This fixed arrangement allows for maximum hydrogen bonding, making ice have the strongest hydrogen bonding among the three forms.
- Liquid Water: In liquid water, hydrogen bonds are dynamic and constantly break and reform due to molecular motion. This results in slightly weaker hydrogen bonding compared to ice.
- Impure Water: Impurities in water disrupt the hydrogen bonding network, further weakening the hydrogen bonding compared to pure liquid water.
Conclusion: The decreasing order of hydrogen bonding is:

To determine which compound will show intramolecular hydrogen bonding, we need to understand the concept of intramolecular hydrogen bonding. Intramolecular hydrogen bonding occurs within a single molecule when a hydrogen atom bound to a highly electronegative atom such as oxygen, nitrogen, or fluorine forms a hydrogen bond with a lone pair of electrons from another electronegative atom within the same molecule. This type of bonding often leads to the formation of a five or six-membered ring.

Given the options:

• : Water molecules exhibit intermolecular hydrogen bonding between different molecules, not intramolecular.
• : Ammonia forms hydrogen bonds with other molecules of ammonia rather than intramolecular hydrogen bonds.
• : Ethanol has the ability to form hydrogen bonds, but these are not intramolecular. The hydrogen of the hydroxyl group forms hydrogen bonds with the oxygen of another ethanol molecule, which is intermolecular bonding.
• The fourth option includes an image of the compound:

The compound depicted in the image is typically salicylaldehyde or orthonitrophenol, which has a hydroxyl group (–OH) and another electronegative group such as an aldehyde (–CHO) or nitro (–NO₂) on adjacent positions. In such compounds, a hydrogen bond can form between the hydrogen atom of the hydroxyl group and the lone pair of electrons on the electronegative atom of the adjacent group, resulting in intramolecular hydrogen bonding.

Conclusion: The depicted compound in the image is correctly identified as having the potential for intramolecular hydrogen bonding. Hence, the correct answer is the compound represented by the image with data-src-id="67347e092f20741705a5c770".

The question asks for the number of molecules that can exhibit hydrogen bonding. Hydrogen bonding occurs in molecules where hydrogen is directly bonded to a highly electronegative atom like nitrogen (N), oxygen (O), or fluorine (F). Let's examine each molecule:

• CH₃OH (Methanol): Contains an OH group. Hydrogen is bonded to oxygen, so it can form hydrogen bonds.
• H₂O (Water): Contains two OH bonds, allowing it to form hydrogen bonds.
• C₂H₆ (Ethane): Lacks N, O, or F bonded to hydrogen, so no hydrogen bonding is present.
• C₆H₅NO₂ (Nitrophenol): Contains an OH group. Hydrogen is bonded to oxygen, allowing hydrogen bonding.
• HF (Hydrogen Fluoride): Contains hydrogen bonded to fluorine, capable of forming hydrogen bonds.
• NH₃ (Ammonia): Contains N bonded to hydrogen, which enables hydrogen bonding.

Counting the molecules that can exhibit hydrogen bonding, we have: CH₃OH, H₂O, C₆H₅NO₂, HF, and NH₃.

Thus, the total number of molecules capable of hydrogen bonding is 5, which falls within the given range [5,5].

This question requires an analysis of the boiling points of ammonia (NH₃) and phosphine (PH₃) in the context of their intermolecular forces, as described in an assertion and a corresponding reason.

Concept Used:

The boiling point of a substance is the temperature at which its vapor pressure equals the pressure surrounding the liquid, and the liquid changes into a vapor. The boiling point is directly related to the strength of the intermolecular forces (IMFs) between the molecules. Stronger IMFs require more energy (and thus a higher temperature) to overcome, leading to a higher boiling point.

The primary types of intermolecular forces relevant here are:

1. Hydrogen Bonding: A special, strong type of dipole-dipole attraction that occurs when hydrogen is bonded to a highly electronegative atom (like Nitrogen, Oxygen, or Fluorine). The hydrogen atom carries a significant partial positive charge and is attracted to the lone pair of electrons on an adjacent electronegative atom.
2. Van der Waals Forces: These are weaker forces that include dipole-dipole interactions and London dispersion forces. They exist in all molecules but are the dominant forces in nonpolar molecules or molecules that cannot form hydrogen bonds.

Step-by-Step Solution:

Step 1: Analyze the Assertion (A).

The assertion states: "PH₃ has lower boiling point than NH₃."

Let's compare the experimentally determined boiling points of these two compounds:

• Boiling point of Ammonia (NH₃) = -33.34 °C (or 239.81 K)
• Boiling point of Phosphine (PH₃) = -87.7 °C (or 185.45 K)

Since -87.7 °C is a lower temperature than -33.34 °C, the boiling point of PH₃ is indeed lower than that of NH₃. Therefore, the statement made in Assertion (A) is true.

Step 2: Analyze the Reason (R).

The reason states: "In liquid state NH₃ molecules are associated through vander waal’s forces, but PH₃ molecules are associated through hydrogen bonding."

Let's examine the intermolecular forces present in each liquid:

• In liquid NH₃: Nitrogen is a small and highly electronegative atom. The N-H bonds are very polar. Consequently, NH₃ molecules can form strong intermolecular hydrogen bonds with each other. While van der Waals forces also exist, hydrogen bonding is the dominant and much stronger force.
• In liquid PH₃: Phosphorus is significantly less electronegative than nitrogen (electronegativity of P ≈ 2.19, N ≈ 3.04). The P-H bond has very little polarity. Due to this low polarity and the larger size of the phosphorus atom, PH₃ molecules are incapable of forming hydrogen bonds. The primary intermolecular forces in liquid PH₃ are the much weaker van der Waals forces (specifically, dipole-dipole and London dispersion forces).

The statement in the Reason claims the opposite: it incorrectly assigns van der Waals forces to NH₃ and hydrogen bonding to PH₃. Therefore, the statement made in Reason (R) is false.

Step 3: Conclude the relationship between Assertion and Reason.

We have established that Assertion (A) is a true statement, but Reason (R) is a false statement. The actual reason for Assertion (A) being true is that NH₃ has a higher boiling point due to the presence of strong intermolecular hydrogen bonds, which are absent in PH₃.

Final Result:

Based on the analysis, Assertion (A) is a correct statement, but Reason (R) is an incorrect statement.

Therefore, the most appropriate answer is: (A) is true but (R) is false.